Challenging the Precious Metal Paradigm

This article was originally published in Caltech’s weekly newspaper, The California Tech.

A team of Caltech scientists and students has discovered a groundbreaking new method of synthesizing carbon-silicon bonds—a method that is easier, cleaner, and a thousand times cheaper than the current state-of-the-art. The Tech sat down with graduate student Anton Toutov and undergrad Kerry Betz, members of the Grubbs lab; and postdoc Wen-Bo “Boger” Liu, a member of the Stoltz lab; to hear the story of how they pursued a seemingly improbable reaction to make a cutting-edge achievement in chemistry.

Lori Dajose: First of all, let’s talk about why your new method is so revolutionary to chemistry.

Kerry Betz: Well, carbon-hydrogen (C–H) bond silylation—replacing a hydrogen atom with a silicon group in a molecule—is normally pretty challenging. You have to use these expensive, rare, and sometimes dangerous metals like platinum, palladium, and iridium, as catalysts. But our reaction uses potassium tert-butoxide as the catalyst. Potassium is naturally abundant, making our compound safe and inexpensive—no more need for those precious metals.

Boger Liu: Additionally, replacing a carbon-hydrogen bond with a carbon-silicon bond is really crucial in making important molecules called organosilanes, chemical building blocks valuable in manufacturing basically everything from new medicines to new functional materials, like next-generation liquid crystals for LCD screens. The idea of making organosilanes catalytically without precious metals seemed so naive and lofty—it was unprecedented. This “precious metal paradigm” was like an axiom in chemistry that few scientists had attempted to challenge.

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From left: Kerry Betz (’15), Anton Toutov, and Wen-Bo “Boger” Liu have recently published a paper detailing the use of potassium tert-butoxide as a catalyst in silylation reactions. Photo courtesy of Allison Maker.

LD: What inspired you to challenge it?

Anton Toutov: Two and a half years ago, I noticed organosilanes occurring as unexpected byproducts from my unrelated experiments with biofuels. It was kind of random, but this really provided the crucial proof-of-principle that we didn’t need to use crazy expensive precious metal catalysts for the carbon-silicon reaction to occur. I just decided to run with it.

LD: And you started looking for people to run with you.

KB: Yes. Around the same time that Anton’s project was gaining momentum, I was looking for summer research. I met with several potential mentors, him included. He was just so incredibly excited and animated talking about it, and I thought, “Wow, he seems like a really fun guy to work with!” I was relatively new to this type of chemistry, so I didn’t have the same bias that more experienced researchers had with regards to this precious metals paradigm.

LD: Boger, you teamed up with Kerry and Anton a few months later. What inspired you to join?

BL: Well, one of the key components of the reaction involves breaking a carbon-hydrogen bond in a heteroarene and replacing it with a carbon-silicon bond. I had done some research on the first half of that process—methods for breaking C-H bonds. Anton and I would have coffee every Saturday, and one day he showed me how he had been using a potassium catalyst for this reaction. I couldn’t believe it. I knew this would change the entire field of C-H silylation chemistry. It was natural for me to get on board with him.

AT: I had worked on the problem alone for some time and solved it to an appreciable degree, and then I knew I could use some really talented and passionate people to help improve the reaction further, and broaden its scope. When Kerry and Boger joined the project, it just took off.

BL: Originally, we began by applying the method to a class of molecules called heterocycles, biologically important scaffolds present everywhere in nature. When it became unbelievably clear that it was really working, we each branched out to apply the method to different classes of molecules.

AT: We were each working in our own direction, simultaneously pushing the project forward on several different fronts. Kerry was making molecules that have never been made before, discovering interesting subtleties about the reaction, and developing some sophisticated hypotheses.  She’s now a completely independent research chemist, and a leading world authority on Earth-abundant metal catalysis, working on extending this method to other molecules. I’m so proud of her. And Boger, he is such an amazing talent. He helped me to optimize the reaction to an excellent level, synthesized a large amount of new molecules using our method, and helped me to develop several new methods based on our general concept. He has also been working on elucidating the mechanism of the reaction, which is currently a big mystery that nobody in the world seems to understand! All in all, I had just the best team imaginable with which I could bring my C–H silylation reaction to life.

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Kerry Betz is the third author on the recent silylation paper. She is an undergraduate in the lab of Professor Robert Grubbs, who won the Nobel Prize in Chemistry in 2005. Photo courtesy of Allison Maker.

LD: Your method isn’t just a new way of synthesizing organosilanes—it’s also a better way than the existing state-of-the-art. Tell me about that.

BL: First of all, we found that the reaction could actually occur under pretty mild conditions. We’re talking room-temperature here—the lowest temperatures this reaction has ever occurred at. In addition, there were no harmful or dangerous byproducts, just hydrogen gas—which is valuable itself!

KB: The method is really environmentally friendly. Using precious metals produces toxic metal waste that has to be filtered out from your desired products—our method has no such drawbacks. On top of being green, it is thousands of times cheaper than using precious metal catalysts. And if being clean and cheap wasn’t enough, it is also pretty easy. This is the kind of thing that could probably be taught in an introductory freshman lab, like Ch3a. It’s shocking how it just blows away this precious-metal paradigm that has been around for almost a century.

LD: Your paper was recently accepted and published in Nature. What was it like for you, to be published in such a prestigious journal?

BL: Well, we got the acceptance email on my birthday. It was a fantastic present.

KB: My birthday was a few days before we got our paper accepted, so it was like a birthday present for me too. I was actually having a really bad day. Then I got a card from Anton saying, “Happy birthday… oh and by the way, congratulations on your publication acceptance into Nature.” It has been so amazing; I’ve been able to help this project come from an uncertain, possibly controversial beginning, to an unprecedented and publishable conclusion.

AT: Yes, and it’s really just the beginning. There’s so much to come, and we are the pioneering lab for this research. Our hope is that this discovery will change the way that people think about chemistry, and about the logic of chemical synthesis in particular.

 

The full paper was published in Nature on February 5, 2015, titled “Silylation of C-H bonds in aromatic heterocycles by an Earth-abundant catalyst.”

The Rusted Red Planet

It is a well-known nuisance that when you leave a freshly sliced apple exposed to air, it quickly turns brown. It’s a nuisance of the same kind that must frustrate the Statue of Liberty—her once-coppery skin turned green from only two years of exposure to air. The process that causes these seemingly dissimilar metamorphoses is called oxidation. Oxidation occurs when an atoms in a substance lose electrons, changing the overall chemical makeup and structure. It doesn’t necessarily cause decay; oxidation is essentially just atomic reshuffling. Key to oxidation processes are atmospheric elements like water and oxygen.

Another common kind of oxidation is rust. Rust occurs when iron metals oxidize to form other compounds. Hematite is one of these results of oxidation, rust-red in powdered form and created by the oxidation of other iron-containing compounds, like magnetite. When magnetite rusts, one of its iron atoms loses an electron, chemically changing into hematite. The presence of water is an important catalyst for this reaction—if you’ve ever left an old bike out in the rain, you’ll notice it gets rusty pretty fast.

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Hematite is the abundant mineral that gives Mars its distinctive reddish color. The planet is covered by a layer of fine red hematite powder, so much so that you can see the hue from Earth on a clear night. But there are no oceans or lakes of water on Mars, and the Martian atmosphere is practically parched. Without water to facilitate rusting and oxidation, the origins of this ubiquitous mineral are unknown. NASA’s Martian rovers have found no indication of rusty Martian bicycle tracks, so there’s one scenario we can rule out.

Mars has a very sparse atmosphere, about 1/100th of Earth’s, and so the surface receives very little protection from solar ultraviolet (UV) radiation. UV light is very powerful: it can split apart molecules to create extremely reactive new molecules called radicals, and it can even interact with our genes to cause mutations. Perhaps the abundance of UV light on Mars, in the absence of water, can facilitate the oxidation of magnetite into hematite.

To test this hypothesis, I placed a few magnetite samples into a chamber with a simulated Martian atmosphere: a very cold, low-pressure CO2 atmosphere with no water vapor. Then I switched on a powerful UV lamp and waited for two weeks. I carried out this research with the Mars Group at the Niels Bohr Institute at Copenhagen University.

There were two possible outcomes.

Possibility 1: Oxidation was detected on the samples at the end of the experiment. This could imply:

  • UV radiation can physically knock electrons off of iron, and alter the ratios of iron and oxygen from magnetite to hematite. No water is necessary. This could mean that the dust on Mars is actively, however slowly, being formed. Mars may not be such a static “dead” planet as we may have thought.
  • UV radiation can interact with CO2 to create an oxidant which then oxidizes iron, changing magnetite to hematite. No water is necessary. Again, this could mean that the dust on Mars is actively, however slowly, being formed.
  • The magnetite in our samples had already been oxidized through exposure to Earth’s atmosphere before we introduced them to our chamber. I’ll explain this more in the results section.

Possibility 2: No oxidation was detected on the samples at the end of the experiment. This could imply:

  • UV radiation cannot induce oxidation alone. It may have no role in converting magnetite to hematite. Alternatively, it may have a partial role combined with mechanical weathering, or other processes. Perhaps the only way UV radiation could have played a role in oxidation is under a completely different set of atmospheric conditions. If Mars previously had an Earth-like atmosphere containing more water and oxygen, UV radiation could photolyze H2O or O2 to create radicals that would steal an electron from iron atoms.
  • UV radiation can indeed induce oxidation without the presence of water, but over very long timescales—the experiment did not run for enough time. This would imply that the dust on Mars could be very old, which suggests that the planet has been unchanging for millions of years.
  • The analysis did not catch the oxidation.

The results are now in.

After the experiment, the samples were analyzed using x-ray photoelectron spectroscopy (XPS). This mouthful is a technique sensitive to the surfaces of materials, giving the chemical composition of the top 10 nanometers. This means that the results we found were only for the surfaces of our samples, not the bulk. XPS can also tell us the chemical environment of an atom, meaning we can determine the oxidation state of elements. The analysis was carried out by Dr. Nico Bovet at Copenhagen University’s NanoGeoScience Center.

The powder samples showed signs of oxidation even before they went in the chamber. The little bump in the graph around 719 eV indicates iron in the oxidized state. After the experiment, they didn’t show any noticeable change.

 

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The spectrum of the powdered magnetite sample before the experiment.

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The spectrum of the powdered magnetite sample after the experiment.

As for the solid samples, neither of them show that same bump around 719 eV — indicating that no iron oxidized after the experiment.

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The spectrum of the solid magnetite sample from Greenland.

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The spectrum of the solid magnetite sample that also included olivine.

So there you have it. Our results indicate that UV radiation cannot, in two weeks, induce the oxidation of magnetite to hematite in an atmosphere analogous to Mars’.

In science, getting “no” for an answer is common, and it’s not necessarily a bad thing. Any result of the scientific process is important, and leads to new questions and new directions of research. It’s possible that UV radiation does play a role in oxidation on longer timescales, or in combination with other Martian processes. We will just have to ask more questions and do more science to find out.

What you’ve all been waiting for: The Experiment

After several weeks of soldering wires and sealing leaks, Rita and I were finally ready to get some Martian simulation going. Because the scientific process should always be transparent, here’s your personal guide to making those lovely irradiated magnetite samples you’ve always wanted.

Now don’t try this at home, kids.

1. Flush the glove box with nitrogen, three times for 15 minutes each. By filling the glove box with nitrogen, we ensured that in the unlikely case of a leak in the chamber, the surrounding atmosphere was unreactive. Rita and I made sure to stand in the hallway when the nitrogen was on, to avoid any unintended unconsciousness.

2. Put the magnetite on the tray and place it into the transfer chamber. We created a vacuum in the chamber, then filled it with nitrogen from the glove box. We did this vacuum-and-fill process three times to make sure no external atmosphere got into the glove box when we transferred in the sample tray. This is important – it’s not a very good Mars simulation chamber if there’s a ton of Earth’s atmosphere in it. We used a glove box that looks like the one below. (Image from Wikimedia Commons.)

 

  • How do you move things around when they’re already in the glove box? The glove box is totally sealed, so we use these awesome built-in gloves to handle the samples once they’re inside. But use caution: wearing these seemingly-invincible contraptions may make you feel and act like a true mad scientist.

3. Take the samples from the transfer chamber, and put them into the simulation chamber. Using our invincibility gloves, we sealed the sample tray inside the small Mars chamber. These are the magnetite samples we used: a chunk from Greenland, a chunk with olivine inclusions, and a very fine powder.

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4. Suffocate the samples. We vacuumed the chamber using first the back pump, and then the turbomolecular pump, so it’s nice and airless. We then let in 18 millibars of CO2 (a millibar is a unit of pressure – one millibar is about the pressure exerted by a penny lying flat). Remember, only the chamber that becomes a vacuum – the surrounding glove box is still filled with nitrogen.

5. Turn on the UV light. You wouldn’t bake a cake without turning on the oven, so why would you even think about doing this experiment without the radiation?

6. SCIENCE HAPPENS! We left the samples under the radiation for two weeks, checking the pressure and UV lights daily to make sure everything was working properly.

On August 11, we removed the samples to be analyzed. I know you’re dying to find out if the radiation mutated our magnetite into miniature Martians, but you’ll just have to wait for the next blog post.

Interstellar Travel on the Starship Hack Circus

About a month ago, I blasted off on the Starship Hack Circus. About fifty other people and I headed towards KOI-3284.01, and I was never to see my friends or family or Earth again. Theoretically.

Hack Circus is an English magazine and podcast about science and technology, and their Starship event coincided with the launch of their newest issue, “First Contact.” The issue is full of interesting and innovative articles — uncontacted tribes on Earth as analogous to intelligent extraterrestrials, how to knit the Arecibo message, and other cosmic quirks. Their launch event was no exception.

For three hours, I participated in an excellent example of creative science communication. Starship Hack Circus presented four experts giving short talks on space exploration and planetary science, but these were far from your traditional lectures — they formed an immersive and interactive experience.

The event wasn’t just “themed”; it took a step further, making you feel like you were on a spaceship bound for an exoplanet. By combining artistic radio technology, speculative SETI, and recordings of stellar and planetary vibrations, the talks were simultaneously informative and attention-grabbing. Audience members weren’t just spectators — we were active participants. We were encouraged to live-tweet during the event using the hashtag #StarshipHackCircus, recording our responses to science in real-time.

In addition to futuristic interplanetary travel, Starship Hack Circus also boldly indicated at another way of the future — science communication’s future.

Starship Hack Circus was an example of the kind of cross-medium sci comm that has the potential to reach millions of people and carry us into the future of learning.  Digital media — blogs, Twitter, Massive Open Online Courses (MOOCs) — are now supplementing and complementing traditional physical media like lectures, textbooks, and papers. Live-tweeting at conferences has become increasingly popular in the last few years, allowing people to keep up with science news from anywhere in the world. We’ve come a long way from monologuing lecturers. Modern science communication is creating a well-rounded database of knowledge that’s accessible to an ever-increasing portion of humanity.

And it’s straight up exciting.

Mechanical Mars – An Interactive Post

When I first saw the Mars chamber I would be working with, I felt just the tiniest sense of utter bewilderment, and possibly a hint of panic. I am not an engineer, and this thing looks mega intimidating.

Thanks to the awesome Rita Kajtar, who made major contributions to the chamber’s construction as part of her masters thesis, I began to understand its various bits and pieces. But still, I knew I’d have a hard time explaining it to you without some visuals. And so, since hands-on learning is the best learning, I made you an interactive photo! Mouseover for some enlightenment.

And here’s the sample tray that goes inside of the Chamber. 

Since science and technology are ever-updating fields, there are of course a few improvements that still need to be made. For example, even though experiments are run under a near-perfect vacuum and condensation is unlikely, a humidity sensor needs to be added. And even though we can use the ideal gas law to make a rough estimate of the temperature during the experiments, it would also be helpful to have a temperature sensor.

The Rocky Road of Experimental Planetary Science

Carl Sagan once said that if you wish to build a Mars chamber from scratch, you must first invent the universe. Ok, maybe he was talking about apple pies, but same thing. [1]

And inventing the universe is what it seems like we’ve been doing the last few weeks. “Simulating the Martian atmosphere” is a much more complex process than just throwing some CO2 into a near-vacuum.

Our “to-do” list is constantly being added to. The UV light needs to be ordered. A cooling system needs to be developed so the light doesn’t overheat. The seal for the chamber needs to be completely airtight to maintain a vacuum, so that condensation doesn’t occur on the cooling system. Wires need to be acquired and soldered in the proper order to provide power to the cooling system. The workshop guys need to be back from vacation to solder the wires.

Most of our work has been on the parts in the box below. It’s the removable sample holder, rigged up with the UV light and Peltier cooling elements to prevent overheating. Since this is where we’ll be putting the magnetite, it’s one of the most precise and crucial parts to get right.

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On the experimental side of planetary science, there’s a lot that can go wrong. Patching up our beloved chamber has taken much improvisation and recycling of parts, and there are times when it feels like we’re just putting band-aids on top of band-aids. But much of the beauty in science comes from the attention to minute details to ensure that our experiment is as close of an approximation to Mars as possible. The process of rigor might be riddled with wrenches and soldering guns, but the end result is actually quite elegant.

I’m looking forward to finally starting our first experiment tomorrow.

1. https://www.youtube.com/watch?v=7s664NsLeFM

Science is Coming

8996 kilometers across a continent and ocean. 18 hours of sunshine per day. 10 weeks. One Mars simulation chamber.

Yep, I’m back in Copenhagen. I’m working on a project with the Mars group at the Niels Bohr Institute, using a Mars simulation chamber to examine the big question: Why is the red planet red? Or, more accurately, how is the red planet red? I’ll be determining whether UV radiation can induce the oxidation of magnetite to hematite, the mineral responsible for Mars’ distinctive shade. I’m very thankful to be funded by the Monticello Foundation at Caltech.

This is my nifty version of Mars in a box.

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Because I’m passionate about reaching a broad audience with my scientific endeavours, I’m starting this blog to document my science shenanigans, from mineralogy in the Mars chamber to my caffeinated attempts at learning Python. Science should be for everyone, so every week I’ll be updating you, and your grandma, and your dog, about what I’m currently working on.

But I’m no world-class researcher (yet). I just finished my third year of undergrad at Caltech, double-majoring in Planetary Science and Philosophy (you might think this is an odd combo — I’ll blog about it soon). I like philosophizing about alien life, experimenting with different genres of journalism, and hunting for the best cappuccinos in Denmark. As an exchange student in Copenhagen last fall, I fell in love with the city and decided to come back for this summer project.

As I’m trying my hand at this science communication thing, there will probably be some typos and inaccuracies throughout — remember, this is my journey through the dark forests of literature searches and experimental trial and error. Science communication is a two-way street, so interaction with you all is important — if you read something that makes no sense or is just plain wrong, write me a comment!

Brace yourselves — science is coming.